In fabricating a friction drive belt exposing its rubber part, normally, component materials of the belt are set on the outer periphery of a cylindrical mold in order from a component material for an outermost belt component. Specifically, the belt component materials are set on the outer periphery of the cylindrical mold by laying them one on another in order of a woven fabric constituting a top fabric, an uncrosslinked adhesion rubber, a twisted yarn constituting a cord, another uncrosslinked adhesion rubber and an uncrosslinked compression rubber. Known as a method for setting an uncrosslinked rubber on the cylindrical mold in such a case is a method of forming an uncrosslinked rubber into a cylindrical rubber and fitting it onto the cylindrical mold.
For example, Patent Document 1 discloses a drive belt fabrication method including: a fabric setting step of fitting a cylindrical fabric subjected to adhesion treatment with rubber cement onto a cylindrical mold; a reinforcing cord setting step of spirally winding a reinforcing cord around the cylindrical mold covered with the cylindrical fabric; and a cylindrical rubber setting step of fitting a cylindrical rubber made of an unvulcanized rubber composition onto the cylindrical mold around which the reinforcing cord is set.
Patent Document 2 discloses a belt fabrication method in which an unvulcanized rubber sheet is heated and pressed with both its ends brought into abutment by a pressing plate to soften it and join both its ends, thereby forming it into a cylindrical form having not level difference at least on one side of the juncture of the ends, and the cylindrical rubber is fitted onto a mold and then vulcanized.
Meanwhile, in belt drive systems in which a drive belt is wrapped, with its back face inside, around a resin-made flat pulley, a problem arises that the flat pulley is worn out by the top fabric of the belt. Therefore, for the belt drive systems, drive belts have been recently employed that have back faces made of short fiber-containing rubber and no top fabrics. In fabricating such a drive belt, a short fiber-containing, uncrosslinked rubber sheet is roundly joined at both ends to form a cylindrical rubber so that the direction orthogonal to the orientation of short fibers is the circumferential direction of the belt, and the cylindrical rubber is set directly around the outer periphery of a cylindrical mold. In this case, in order that the cylindrical rubber does not get wrinkled when a twisted yarn constituting a cord is wound around it, the cylindrical rubber must be formed with a size that causes no sag from the cylindrical mold. Particular attention is needed when the cylindrical rubber is made of a low-tack rubber material.
However, when the cylindrical rubber is formed to cause no sag from the cylindrical mold, it receives a circumferential tension, which may break the joining at the rubber juncture.
Patent Document 1: Published Japanese Patent Application No. 2000-334856
Patent Document 2: Published Japanese Patent Application No. 2001-121619